The alphaepsilonBeta integrin is expressed selectively on mucosal lymphocytes. While it is known that alphaepsilonBeta binds to E- cadherin expressed on epithelial cells in vitro adhesion assays, the in vivo functions of alphaepsilonBeta remain unknown. In preliminary studies, mice which lack alphaepsilon expression have been generated by gene targeting. These alphaepsilon animals have reduced numbers of intestinal intraephithelial lymphocytes and lamina propria lymphocytes. In addition, in an in vivo model of inflammatory bowel disease, CD 4/CD4+5RBhi cells isolated from bethaepsilon mice produced less severe intestinal inflammation than cells isolated from alphaepsilon+/+ mice. Thus, alphaepsilonBeta appears to play an important role in the development of intestinal inflammation. However, the mechanisms whereby alphaepsilon deficiency results in these changes are not clear, as integrins expressed on peripheral blood lymphocytes are known to be important in T lymphocyte extravasation/localization, development, and to act as co- stimulatory/adhesion molecules modulating the functional response of T cells to antigenic challenge. Indeed, integrins often mediate more than one function when expressed on T lymphocytes. In this application, studies are proposed to define the function(s) of alpha epsilon Beta. In aim 1, iIEL development in alphaepsilon Beta mice will be evaluated by FACS analysis of T lymphocyte subpopulations and analysis of the iIEL cell receptor repertoire. In aim 2, the adhesion of alphaepsilon Beta and alphaepsilon+/+ iIEL to recombinant E-caderin, lamina propria endothelial cells, and lamina propria interstitium will be evaluated, and the in vivo localization of alphaepsilonBeta and alphaepsilon+/+ iIEL will be compared in adoptive transfer experiments. In aim 3, the impact of alphaepsilon expression on lymphocyte functions including proliferation, cytokine production, cytotoxicity and T cell regulation of Beta cell immunoglobulin class switch will be determined, and the proportion of iIEL proliferating in vivio in alphaepsilon+/+ and alphaepsilon-/- mice will be compared. Finally, in aims 4 and 5 the impact of alphaepsilonbeta expression in the mucosal immune response to infection will be evaluated with in vitro and in vivo functional studies using T. spiralis infection as a model. These studies will provide important information about the in vio function(s) of the alphaepsilonbeta integrin and will used in evaluating the potential of blocking alphaepsilonbeta function as a treatment for IBD.